1. Field of the Invention
The present invention relates to a reflective optical element, especially to a reflection film formed on the reflection plane of the reflective optical element.
2. Description of the Related Art
Thin films of metals such as aluminum and silver having a high reflectivity have been used for the reflection film to be formed on the reflection plane of conventional reflective optical elements. Silver has so high a reflectivity at the visible wavelength region, that it is frequently used for mirrors and reflective optical elements.
The thin films of metals such as aluminum and silver have been usually deposited by vacuum deposition, sputtering and ion plating.
While the metallic thin film to be formed on the reflection plane of the reflective optical element may be used as a monolayer, it may be laminated with an antioxidation film for preventing the metallic thin film from being oxidized, and a reflection increment film for improving reflective characteristics of the metallic thin film.
However, the reflective optical elements and reflection films as described in the prior art have problems.
First, durability and abrasion resistance of the metallic thin film should be improved.
It is also a problem that the surface of the metallic thin film is liable to be oxidized to form a metal oxide film by an oxidation reaction, reducing its reflectivity.
Decrease of reflectivity due to the oxidation reaction of the metal surface tends to be accelerated by deposition of moisture on the surface of a metal when the film is placed in an environment of room temperature and ambient humidity after it has been allowed to stand in a high temperature and high humidity atmosphere for a long period of time, or when the film is abruptly exposed to a cold environment.
Since the metallic thin film, especially the silver thin film, has a soft surface, abrasion resistance of the film becomes very low when the film is used while its surface is exposed to outside, failing to obtain a desired reflectivity due to abrasion of the metallic thin film.
Accordingly, the object of the present invention is to provide a reflective optical element whose reflectivity is not decreased by allowing it to leave in a high temperature and high humidity condition for a long period of time.
Another object of the present invention is to provide a reflective optical element having good abrasion resistance.
In one aspect, the present invention provides a reflective optical element having at least one or more of metallic thin layers on a monolayer or a multi-layer of the thin film layers formed on a peripheral surface of a transparent substrate to obtain a desired reflection of light by allowing the light incident from the transparent substrate side, or the light advancing in the transparent substrate, to reflect with the metallic thin film, wherein the thin films formed on the peripheral surface of the transparent substrate comprise the metallic thin film and an amorphous fluorocarbon resin laminated from at least the transparent substrate side. Laminating the amorphous fluorocarbon resin on the metallic thin film in the present invention provides a reflective optical element whose metallic thin film has good durability and abrasion resistance.
The metallic thin film formed on the peripheral surface of the reflective optical element is coated with a resin layer comprising the amorphous fluorocarbon resin in the reflective optical element according to the present invention to render the thin film water-repelling property with the amorphous fluorocarbon resin, thereby moisture adhered on the surface of the optical element does not reach the metallic thin film situated inside of the amorphous fluorocarbon resin. It is also made possible to reduce deposition of moisture on the surface of the optical element accompanied by environmental changes such as from an environment of high temperature and high humidity to an environment of room temperature and ambient humidity, or from an environment of room temperature and ambient humidity to a cold environment. These effects allow formation of metal oxides due to an oxidation reaction of the metallic thin film to reduce, preventing reduction of reflectivity of the metallic thin film caused by forming metal oxides. Also, it is made possible to improve abrasion resistance of the metallic thin film by coating the periphery of a film having a soft surface such as a thin film of silver, enabling durability of the optical element to be improved.